Areas
Areas of some well-known figures are given below:
Ex.1 A horizontal pipe for carrying floodwater
has diameter 1 m. When water in it is 10 cm
deep then the width of water surface AB is equal
to ________ cm.
(1) 10 cm
(2) 25 cm
(3) 60 cm
(4) 70 cm
(5) None
Sol.
Let O be the centre of circle.
In ΔOAD
502 = 402 + x2
2500 – 1600 = x2
x2 = 900
x = 30
∴ AB = 2x = 60 cm. Answer: (3)
Ex.2 Area of the shaded region is
(5) None of these
Sol.
Volume
Length of a diagonal:
The length of diagonal of a cuboid =
The length of a diagonal of a cube =
Ex.1 An insect is crawling to climb a 20 metre long pipe of diameter 3.5 metres. If the insect take 4
circular rounds to reach the top of the building, then what will be total distance (in nearer
metres) traveled by insect to reach the top?
(1) 47 m
(2) 48 m
(3) 49 m
(4) 50 m
Sol. Since the insect is moving in circular way, so it will cover the distance which will be 4 times the distance
of the longest side AB of a right angled triangle. In the figure AO is equal to the circumference of the
pipe.
AO = πd = = 11m
BO = 5 m
AB = =
= 12.08 m
Total distance traveled = 12.08 × 4 = 48.32 m
Hence distance in nearer meters = 48 m
Ex.2 The surface area of a cube is 726 sq metres. Find the volume of the cube.
(1) 1234 m2
(2) 1431 m2
(3) 1341 m
(4) 1331 m
(5) None of these
Sol. Surface area S = 726 m2 Volume V = ?
In a cube,
S = 6a2 = 726 ⇒ a2 = 121 ⇒ a = 11 m
So, V = a3 = 113 = 1331 m3. Answer: (4)